It’s not easy starting over. X-Men: First Class found that out on Friday as it grossed $21 million, according to early estimates. While that’s a debut many movies would die for, it’s a disappointment compared to other X-Men and Marvel movies.

The original X-Men brought in nearly the same amount ($20.8 million) its opening day, but that was way back in 2000. In today’s dollars, X-Men’s opening would rise to $30.3 million. The other X-Men entries – X2: X-Men United, X-Men: The Last Stand, and X-Men Origins: Wolverine – earned $31.2 million, $45.1 million, and $34.4 million on their first days. This is simply a lengthy way of saying that First Class had the smallest opening-day attendance of the series. It also fell short of other recent Marvel-based films, including Thor ($25.5 million) and The Incredible Hulk ($21.5 million). However, Fox’s reboot of the mutant-superhero franchise did earn the series’ best reviews since X2, so there’s a chance the $160 million action film will hold up well the following weeks. For this weekend, however, First Class will have to settle for about $54 million.

Most holdovers witnessed significant drops from last weekend’s Memorial Day frame. The Hangover Part II plunged 65 percent for $10.5 million. The R-rated comedy sequel is on pace for a $33 million weekend, which would push the Wolf Pack’s two-week total past $187 million. In third, Kung Fu Panda 2 descended 52 percent, which is surprising considering it’s the only children’s film in wide release. With an estimated $23 million gross this weekend, Panda 2 will have accumulated a little less than $100 million in two weeks. By comparison, the first Kung Fu Panda movie had tallied $117.3 million after two weekends. Pirates of the Caribbean: On Stranger Tides fell to fourth place with $5.1 million – a 53-percent drop. Bridesmaids, on the other hand, continued to show off its stamina by slipping only 23 percent for $3.6 million. The R-rated wedding comedy will cross $100 million today.